pirochetes that were originally isolated from Ixodes spp. icks are the etiological agents of Lyme disease, erythema hronicum migrans and tick-associated chronic meningitis. Our tudies of the pathogenesis of Lyme disease and related isorders have focused on proteins that are immunogenic during uman infection and the surface components of the spirochete. e have to date identified in the Lyme disease spirochetes hree major antigens, two of which are abundant surface roteins. The genes for these two surface proteins have been loned into Escherichia coli. Monoclonal antibodies specific or each of the three antigens were developed. Monoclonal ntibodies againts one of the surface proteins differed in heir reactivities with different isolates. There appear to be t least four distinct serotypes among the strains examined. hese studies and the reagents we have developed have provided ome understanding of the antigenic "make-up" of these pirochetes and will provide the basis for further nvestigations on the pathogenesis of these acute and chronic acterial diseases.